Three-Layer NOx Adsorber Catalyst for Consistent Emission Control
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Solution Overview
Problem
Conventional lean NOx trap catalysts exhibit inconsistent performance between activated and deactivated states, leading to challenges in engine calibration and poorer emissions profiles due to varying activity levels over the catalyst's lifetime and in response to short-term changes in exhaust gas composition.
Innovation Solution
A lean NOx trap catalyst comprising three layers: a first layer with platinum group metals, ceria-containing material, and an alkali or alkaline earth metal supported on an inorganic oxide; a second layer with noble metals and a second ceria-containing material on another inorganic oxide; and a third layer with noble metals having reducing activity on a third inorganic oxide, which separates NOx storage and oxidation functions for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional lean NOx trap catalyst is used, then the catalyst can store and release NOx, but the performance varies significantly between activated and deactivated states leading to inconsistent emissions control
Solution Approach 1:
The catalyst is divided into three distinct functional layers: a first layer with Pt/Pd for oxidation, a second layer with Ba for NOx storage, and a third layer with Rh for reduction. This segmentation allows each layer to perform its specific function optimally, ensuring consistent performance regardless of the overall catalyst state, as each layer responds predictably to its designated chemical processes.
Solution Approach 2:
Different regions of the catalyst (the three layers) are given different chemical compositions and functionalities tailored to their specific roles. The oxidation layer contains Pt/Pd for oxidizing CO and HC, the storage layer contains Ba for trapping NOx, and the reduction layer contains Rh for converting NOx to N2. This local differentiation ensures each region maintains optimal performance characteristics.
2Productivity
If the catalyst operates below its operating temperature (cold start), then the emission control system is relatively inefficient, but increasing temperature to improve efficiency may lead to other issues
Solution Approach 1:
The catalyst is designed to be effective across a broad temperature range by selecting materials with appropriate thermal properties. The Ba-based storage material and Rh-based reduction catalyst maintain activity at lower temperatures, allowing the system to achieve good emission control efficiency during cold start conditions without requiring high operating temperatures.
3Reliability
If a three-layer structure is implemented to separate functions, then NOx storage and oxidation performance are improved, but the device complexity increases
Solution Approach 1:
The catalyst is divided into three distinct functional layers: a first layer with Pt/Pd for oxidation, a second layer with Ba for NOx storage, and a third layer with Rh for reduction. This segmentation allows each layer to perform its specific function optimally, ensuring consistent performance regardless of the overall catalyst state, as each layer responds predictably to its designated chemical processes.
Solution Approach 2:
The three-layer structure integrates multiple functions within a single catalyst component. The first layer performs oxidation of CO and hydrocarbons, the second layer stores NOx, and the third layer reduces NOx to nitrogen. This multi-functionality eliminates the need for separate catalyst components, simplifying the overall emission control system despite the internal complexity of the layered structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The catalyst demonstrates enhanced NOx storage properties and CO oxidation activity, maintaining improved performance in both lean and rich conditions, and achieves consistent performance across its lifecycle and varying exhaust gas compositions.
Implementation Method 1
nitric oxide reacts with oxygen to produce NO2 in the presence of the oxidation catalyst
Implementation Method 2
the NO2 is adsorbed by the NOx adsorbent in the form of an inorganic nitrate
Implementation Method 3
the stored inorganic nitrates decompose to form NO or NO2 which are then reduced to form N2 by reaction with carbon monoxide, hydrogen and/or hydrocarbons in the presence of the reduction catalyst
Data Source
AI summary
A lean NOx trap catalyst and its use in an emission treatment system for internal combustion engines is disclosed. The lean NOx trap catalyst comprises a first layer, a second layer, and a third layer.